detect/dataset: skip adding localstatedir if fullpath is provided

When the option to set a full path is enabled and a full path is
provided, skip adding the prefix (based on localstatedir) to the
directory since it would be unexpected and unwanted by a user.

Ticket: 7083

src/detect-dataset.c

@@ -330,12 +330,15 @@ static int SetupSavePath(const DetectEngineCtx *de_ctx,
     const char *dir = ConfigGetDataDirectory();
     BUG_ON(dir == NULL); // should not be able to fail
     char path[PATH_MAX];
-    if (snprintf(path, sizeof(path), "%s/%s", dir, save) >= (int)sizeof(path)) // TODO windows path
-        return -1;
 
-    /* TODO check if location exists and is writable */
+    if (!PathIsAbsolute(save)) {
+        if (snprintf(path, sizeof(path), "%s/%s", dir, save) >= (int)sizeof(path)) // TODO windows path
+            return -1;
+
+        /* TODO check if location exists and is writable */
 
-    strlcpy(save, path, save_size);
+        strlcpy(save, path, save_size);
+    }
 
     return 0;
 }